1. Field of the Invention
The present invention is directed to a fastener, fastener joint, and a method for reducing stress in an internal combustion engine component.
2. Description of Related Art
Various designs for threaded fasteners are known for addressing different problems associated with fasteners. For example, U.S. Pat. No. 4,973,209 to Essom et al. discloses a screw for use in contaminated pre-tapped holes. The reference discloses a locking screw having a head at one end, a special entry portion at the other end, and a trilobular shank portion extending from the entry portion toward the head. The screw is disclosed as having a thread profile that is of a double angle configuration, and having an entry section that is tapered and formed with a series of truncations which serve to clear progressively, a contaminating coating in an internally threaded workpiece, such as a nut.
U.S. Pat. No. 6,120,227 to Murase et al. discloses a self-aligning bolt that corrects misalignment of the bolt even when the bolt is inserted slanted into a mating hole or a nut. The reference discloses that the bolt includes a constant diameter columnar portion having a diameter smaller than that of a bolt shank portion. The columnar portion is disclosed as being formed on an end portion of the bolt shank portion, and includes a short tapered portion therebetween.
U.S. Pat. No. 4,090,544 to Bagheri et al. discloses a self-locking screw fastener with at least one radially outwardly protruding lobe which serves to lock the screw fastener when in use. The screw fastener is disclosed as having an externally screw threaded fastener body with a longitudinal bore with a reduced inner axial portion and an outer axial portion of enlarged diameter. The reference further discloses that to form the protruding lobe, a noncircular mandrel is forced into the bore to expand the reduced inner portion thereof.
Numerous different fasteners have been used for internal combustion engine components. These different fasteners secure various engine components together to allow the engine to function properly. Many fasteners are subjected to high torque to tightly secure internal combustion engine components together, and are subjected to significant clamping loads. For example, main bearing bolts are used to secure bearing caps to the engine block. Cylinder head studs and/or bolts are used to tightly secure the cylinder head to the engine block. In both of these applications, high torquing of the fasteners is required to establish high clamping loads, and the fasteners are subjected to high cyclical loads caused by the operation of the internal combustion engine.
After long periods of use, it has been found that stress crack and joint failure can occur in the internal combustion engine components at these locations. In this regard, such failures have been found especially when the fastener joint is subjected to additional stress. For example, in continuing to improve their products, an engine manufacturer may increase the power or torque output of their internal combustion engine by increasing the cylinder pressures. This may be attained through various ways, including modification of the internal combustion engine or by optimizing engine operational parameters. Such increase in cylinder pressures of internal combustion engine has been found to cause stress cracks at the threads engaged by the main bearing. If such stress cracking and joint failure occurs in the engine block, the repair can be extremely expensive. Therefore, there exists an unfulfilled need for a method for reducing stress failures at fastening joints in an internal combustion engine that can be caused by cyclical loading of highly torqued fasteners when cylinder pressures are increased.